1. Field of the Disclosure
The disclosure herein relates generally to mills for milling casings in a wellbore and specifically to mills that include an apparatus that may be used to break-up the cuttings (swarf) created by the mills during upward milling of the casings.
2. Background of the Art
Wellbores are drilled in subsurface formations to produce hydrocarbons (oil and gas). Modern wells can extend to great well depths, often more than 15,000 ft. A wellbore is typically lined with casing (a string of metal tubulars connected in series) along the length of the wellbore to prevent collapse of the formation (rocks) into the wellbore. A variety of devices are installed in the wellbore to produce the hydrocarbons from the formation surrounding the wellbore from one or more production zones. Sometimes it is necessary to mill a section of the casing to perform a downhole operation, such as forming windows for forming lateral wellbores, abandoning wells, etc. To perform a milling operation, a tool (commonly referred to as a mill), with cutting members (also referred to as knives or blades) is typically conveyed inside the casing by a tubular. In one type of mills, the mill is activated and pulled upward (uphole) to cut the casing into cuttings (also referred to as “swarf”). The cuttings are often in the form of strings and tend to accumulated in the space between the mill and the wellbore.
The disclosure herein provides mills that include an apparatus attached below the cutters of the mill that breaks-off the cuttings and aids such cuttings to fall into the wellbore below the mill as the mill is pulled uphole.